The present invention relates generally to the field of bearings. More particularly, the invention relates to hydrodynamic sleeve bearings having thrust capabilities, and even more specifically to a novel arrangement for providing lubrication and increasing the load capacity of such bearings.
A wide variety of bearings are available and are currently in use throughout a range of industrial applications. Bearings are generally used to facilitate rotational movement in a mechanical application. In general, a typical antifriction bearing includes a plurality of bearing elements between races or rings situated in a housing. Other bearings include simple journals or other bearing surfaces. Depending upon the application and the anticipated loading, various types of elements may be employed for the actual load-bearing elements. These may include journals, needles, rollers, balls, and so forth.
A journal bearing, also known as a sleeve bearing, is formed from a plain cylindrical sleeve that carries a rotating shaft. Sometimes, journal bearings are also referred to as fluid film bearings because of the presence of a thin film of lubricant formed between the cylindrical sleeve and the rotating shaft. The coefficient of friction experienced by the rotating shaft is dependent, in large part, on whether a fluid film is fully developed. In essence, a fully developed fluid film creates a hydrodynamic pressure sufficient to float the shaft and its respective load relative to the sleeve or journal. The result of a fully developed fluid film is that there is no physical contact between the rotating shaft and the journal during operation. Proper development of a fluid film is generally dependent on adequate lubrication of the bearing journal.
While bearings are often thought of in terms of restricting radial movement while allowing rotation of a shaft, bearings can also be configured to restrict the axial movement of the shaft. Such bearings are typically referred to as thrust bearings or bearings with thrust capacity. Thrust bearings typically operate at lower speeds than their non-thrust bearing counterparts. The general principle behind a thrust bearing is to provide a surface against which a shoulder or other element of a shaft or collar may bear. The simplest way to accomplish this is to form a thrust ring as an integral part of the bearing assembly. The thrust ring is often fixed in some way to the bearing housing and has an annular surface against which a shoulder or collar may bear as it rotates. In certain designs, the thrust ring is broken into sections which, when placed together, form a substantially annular surface for the shoulder or collar to bear against. Lubrication is introduced across the working face of the thrust ring to reduce associated friction. However, frictional loads tend to be relatively high in thrust bearings.
One manner of improving the frictional characteristics of a thrust bearing is to place grooves into the thrust ring surface. Lubricant is then introduced to the surface of the thrust bearing through the grooves, which allows an oil film to develop between the bearing ring and the collar of the shaft similar to that of the journal bearing. Other designs have also been employed to reduce associated friction, to increase the thrust capacity, and to increase the overall efficiencies of thrust bearings. Such designs include segments with a stepped surface, segments with a tapered surface, and segments which may tilt and self-adjust. Each design brings both advantages and complexities.
For example, a stepped bearing is a relatively simple design and relatively inexpensive to produce. The step bearing is essentially a flat bearing with a portion of the surface or a portion of the surface of each segment stepped down. The stepped down portion is not in working contact with the shoulder or collar, and thus the working surface area is reduced. This design may also aid in lubrication by creating a location from which lubricant may be introduced to the working surface. However, because step bearings are inherently sensitive to misalignment between the bearing and shaft, and because of the reduced area of the working surface, step bearings are typically used only on bearings of smaller sizes.
The tapered bearing on the other hand, may be used on larger bearings, but becomes more expensive to manufacture and still has some sensitivity to alignment. Tapered bearings are similar to step bearings, but included tapered portions rather than stepped portions. Oil grooves are often placed adjacent the tapered portion to assist with lubrication. The tapered design is more efficient than the stepped design at introducing lubrication and developing a film between the collar and working surface of the bearing.
The tilting pad bearing, sometimes referred to as a Kingsbury thrust bearing, has high thrust capabilities and the ability to absorb significant amounts of misalignment. However, the Kingsbury thrust bearing is more complex and costly to produce than the previously mentioned bearing types. The bearing members in this type are tiltable shoes (segments) which rest on hard steel buttons mounted on the bearing housing. The members can freely tilt with the steel button as a pivot point. The members tilt during rotation of the collar and help to form a wedge-shaped oil film between the shoe surface and the collar of the shaft. Again, the shape of the shoes are typically such that, when placed together, they form a substantially annular ring on which the shoulder or collar bears.
One concern with thrust bearings, regardless of the design utilized, is proper lubrication. In addition to proper fluid film development, mentioned above, adequate lubrication has other related and consequential benefits. For example, it is commonplace to equip a thrust bearing with a means for lubricating the thrust ring (or segments) during operation, to prolong the useful life of the thrust ring. This is typically accomplished by providing a synthetic or mineral lubricant, such grease or oil, to coat the surfaces of each thrust ring segment. The application of grease or oil serves to preclude the ingress of contaminants, such as dirt, debris, moisture, and so forth. Another advantage provided by proper lubrication is the cooling of the thrust components during operation. Temperature control is an important consideration in bearing design and selection. In particular, temperature control plays an important role in determining expected life of a bearing and the associated thrust components. Likewise, a thrust bearing load capacity is strongly correlated to temperature of the thrust components. Various methods are utilized to provide proper lubrication to the thrust components in an attempt to obtain these benefits. However, improved lubrication is always desirous in a thrust bearing.
There is a need, therefore, for an improved bearing which efficiently and effectively provides thrust capacity. There is also a need to provide proper lubrication with greater temperature control for such a bearing.
In accordance with one aspect of the present technique, a bearing assembly is provided which includes an annular support member and a plurality of thrust bearing elements coupled to and distributed about the face of the support member. The thrust bearing elements are adapted to receive and support an axial load of a rotating member such as a thrust collar on a shaft. An annular distribution ring is mounted to the face of the support member. A distribution passage is formed between the distribution ring and the support member in such a manner that the distribution passage carries fluid to and across each of the thrust bearing elements.
The bearing assembly may further include a feed port in communication with the distribution passage which is adapted to receive fluid from an external source. A retainer ring and feed port may be arranged such that the fluid has a first flow rate as it is introduced at the feed port and second increased flow rate as it enters the distribution passage. The feed port may further be designed to be in parallel communication with the distribution passage and a lubrication channel for a main radial bearing.
In accordance with another aspect of the technique, a distribution ring is provided to provide efficient lubrication and cooling to a plurality of thrust bearing elements. The distribution ring includes a distribution passage which is in communication with the thrust bearing elements. The ring may be designed to include various features and benefits as described with the above bearing assembly.
In accordance with yet another aspect of the technique, a method is provided for distributing fluid to a plurality of thrust members coupled to a support member in a thrust bearing. A substantially annular member has a plurality of openings for receiving the plurality of thrust members. The substantially annular member is coupled to the support member and a distribution passage is formed between the substantially annular member and the support member. A fluid is introduced through the distribution passage to, and across, each of the thrust members. The fluid is introduced from an external source through a feed port which may be in parallel communication with the distribution passage and a lubrication channel for a main radial bearing. The feed port and distribution passage may also be adapted such that the fluid has a first flow rate as it is introduced at the feed port and second increased flow rate as it enters the distribution passage.